Dye-salt separation membrane and preparation method thereof

ABSTRACT

The present invention relates to a dye-salt separation membrane and a preparation method thereof. The method includes the following steps: firstly pouring an aqueous phase solution containing tannic acid and anhydrous piperazine on a surface of a polysulfone-based ultrafiltration base membrane at a mass ratio of the tannic acid to the anhydrous piperazine of 1:2 to 2:1, followed by complete infiltration, and draining the aqueous phase solution; and then pouring an organic phase solution of trimesoyl chloride on the surface of the base membrane, and draining the organic phase solution to obtain the dye-salt separation membrane. The method of the present invention is simple and easy to implement, and the dye-salt separation membrane prepared by the method has a relatively high solution permeability, an efficient dye retention and permeability of inorganic salts, thereby achieving an excellent dye-salt separation effect.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of China application serialno. 201910545384.8, filed on Jun. 22, 2019. The entirety of theabove-mentioned patent application is hereby incorporated by referenceherein and made a part of this specification.

BACKGROUND Technical Field

The present invention belongs to the technical field of nanofiltrationmembranes, and relates to a dye-salt separation membrane and apreparation method thereof.

Description of Related Art

Dye-salt separation technology is a membrane technology for watertreatment, which is mainly used to treat salt-containing dye wastewater.This technology uses a nanofiltration membrane which has a structurethat is generally more loose than that of the traditional nanofiltrationmembrane, enabling effective retention of organics, such as organicdyes, with a molecular weight of 200-1000 Da, while allowing inorganicsalts, such as sodium sulfate and sodium chloride, to pass throughmembrane pores, thereby achieving effects of separating the dyes fromsalts in wastewater to recover the salts and water in it (J. Membr. Sci.2015, 477, 183-193).

At present, methods used to prepare a dye-salt separation membranemainly include interfacial polymerization method. The interfacialpolymerization is carried out by dissolving two monomers separately inan aqueous phase and an oil phase immiscible with each other, andperforming a polycondensation reaction at the interface of the twosolutions. In the traditional interfacial polymerization reaction, themonomer for the aqueous phase commonly used includes m-phenylenediamine,anhydrous piperazine, tannic acid and the like (Environ. Sci. Technol.2019, 53, 1296-1304; Mater. Chem. Front., 1 (2017) 1028-1040; and J.Membr. Sci. 541 (2017) 137-142), and the monomer for the oil phasecommonly used includes trimesoyl chloride (Environ. Sci. Technol. 2019,53, 1296-1304). However, membranes prepared by the traditionalinterfacial polymerization usually have a high retention rate for bothdyes and inorganic salts, thus not only leading to excessive osmoticpressure on the membrane surface which causes low water flux, but alsolosing opportunities to recover the inorganic salts from salt-containingdye wastewater when treating the wastewater, which will cause waste.Therefore, preparation of a dye-salt separation membrane capable ofseparating dyes from salts has become an emerging research direction.

Existing methods are different from the interfacial polymerizationmethod used for preparing the traditional nanofiltration membrane inthat when preparing the dye-salt separation membrane, in the existingmethods, it is necessary to design and use brand-new polyamine monomersfor interfacial polymerization (Environ. Sci. Technol. 2017, 51,9252-9260), or to introduce appropriate nano-fillers in the traditionalinterfacial polymerization method to loosen the structure of theobtained membrane (J Membr. Sci. 2017, 539, 128-137). However, thedesign and synthesis of the new monomer molecules will complicate thepreparation process of the dye-salt separation membrane, and theintroduction of the nano-fillers will cause the fillers to be lost fromthe membrane during a filtration process, resulting in the risk ofsecondary contamination.

SUMMARY

An object of the present invention is to provide a dye-salt separationmembrane which is simple and easy-to-use, and has an excellentseparation effect, and a preparation method thereof.

The objective of the present invention is achieved by the followingtechnical solutions.

The present invention provides a method for preparing a dye-saltseparation membrane by using a mixture of piperazine and tannic acid asa solute in an aqueous phase solution to react phenolic hydroxyl groupof the tannic acid with amino group of the piperazine in water to form alonger monomer for aqueous phase, which is then subjected to interfacialpolymerization with an organic phase solution of trimesoyl chloride on ahigh polymer ultrafiltration base membrane, the method specificallyincluding the following steps:

step 1: pouring an aqueous phase solution containing tannic acid andanhydrous piperazine on a surface of a polysulfone-based ultrafiltrationbase membrane at a mass ratio of the tannic acid to the anhydrouspiperazine of 1:2 to 2:1, followed by complete infiltration for 3 to 6minutes, and then draining the aqueous phase solution;

step 2: pouring an organic phase solution of trimesoyl chloride on thesurface of the polysulfone-based ultrafiltration base membrane obtainedin step 1, followed by complete infiltration for 0.5 to 2 minutes, thendraining the organic phase solution, and after the organic phasesolution being completely evaporated, storing the resulting dye-saltseparation membrane in water.

Preferably, in step 1, the polysulfone-based ultrafiltration basemembrane is selected from polyethersulfone, polysulfone, or sulfonatedpolyethersulfone.

Preferably, in step 1, the aqueous phase solution contains the tannicacid and the anhydrous piperazine at a combined mass fraction of 0.2 wt%.

Preferably, in step 1, the infiltration is performed for a time periodof 5 minutes.

Preferably, in step 1, the mass ratio of the tannic acid to theanhydrous piperazine is 1:1.

Preferably, in step 2, the organic phase solution of the trimesoylchloride contains the trimesoyl chloride at a mass fraction of 0.1 wt %.

Preferably, in step 2, the infiltration is performed for a time periodof 1 minute.

Preferably, in step 2, the organic phase solution contains a solventselected from n-hexane or cyclohexane.

The present invention also provides a dye-salt separation membraneprepared by the above-mentioned preparation method.

The present invention has the following advantages over the prior art.

(1) The present invention adopts the method in which the readilyavailable tannic acid and piperazine are reacted in advance, simplifyingthe preparation process of the dye-salt separation membrane, while anynano-fillers are not introduced, thereby avoiding the risk of secondarycontamination due to the loss of the fillers.

(2) The method according to the present invention is simple and easy toimplement, and for the longer monomer for the aqueous phase formed bythe phenolic hydroxyl group of tannic acid reacting with the amino groupof piperazine in water, regardless of whether the terminal of themonomer is the amino group of piperazine or the phenolic hydroxyl groupof tannic acid, the monomer can undergo the interfacial polymerizationwith polyacyl chloride to enlarge pores in the membrane obtained by theinterfacial polymerization, achieving a dye-salt separation effect.

(3) The dye-salt separation membrane according to the present inventionhas a relatively high solution permeability (up to 315.2 Lm⁻²h⁻¹MPa⁻¹),an efficient dye retention (retention rate of Congo red dye up to99.42%) and permeability of inorganic salts (permeability of sodiumchloride up to 94.59%; and permeability of sodium sulfate up to 89.69%),thereby achieving an excellent dye-salt separation effect. In addition,in the case where the dye retention and salt permeability are comparableto those in the prior art, water flux is significantly improved.

DESCRIPTION OF THE EMBODIMENTS

The present invention will be further described below with reference toExamples.

Example 1

Step 1: An aqueous phase solution containing a mixture of tannic acidand anhydrous piperazine as a solute at a combined mass fraction of 0.2wt % was formulated. The mass ratio of tannic acid to anhydrouspiperazine in the mixture was 1:2. After the formulation of the aqueousphase solution was completed, the aqueous phase solution was poured on asurface of a polyethersulfone ultrafiltration membrane and allowed tocompletely infiltrate it for 5 minutes, and then, the aqueous phasesolution was drained.

Step 2: A solution containing trimesoyl chloride as a solute in n-hexaneat a mass fraction of 0.1 wt % was formulated. After the formulation wascompleted, the solution was poured on the surface of thepolyethersulfone ultrafiltration membrane treated in step 1 and allowedto completely infiltrate it for 1 minute, and then the organic phasesolution was drained. After the organic phase solution was completelyevaporated, the resulting dye-salt separation membrane was placed indeionized water for storage.

Separation performance test 1: The resulting dye-salt separationmembrane was installed in a membrane separation device in which thedifferential pressure across the membrane was controlled to 0.4 MPa, andit was determined that at room temperature, for a dye-salt aqueoussolution containing 0.2 g/L of Congo red and 2 g/L of sodium chloride,the retention rate of Congo red was 99.48%, the permeability of sodiumchloride was 93.98%, and the permeate flux was 249.4 Lm⁻²h⁻¹MPa⁻¹.

Separation performance test 2: The resulting dye-salt separationmembrane was installed in a membrane separation device in which thedifferential pressure across the membrane was controlled to 0.4 MPa, andit was determined that at room temperature, for a dye-salt aqueoussolution containing 0.2 g/L of Congo red and 2 g/L of sodium sulfate,the retention rate of Congo red was 99.64%, the permeability of sodiumsulfate was 87.02%, and the permeate flux was 225.5 Lm⁻²h⁻¹MPa⁻¹.

Example 2

Step 1: An aqueous phase solution containing a mixture of tannic acidand anhydrous piperazine as a solute at a combined mass fraction of 0.2wt % was formulated. The mass ratio of tannic acid to anhydrouspiperazine in the mixture was 2:1. After the formulation of the aqueousphase solution was completed, the aqueous phase solution was poured on asurface of a polyethersulfone ultrafiltration membrane and allowed tocompletely infiltrate it for 5 minutes, and then, the aqueous phasesolution was drained.

Step 2: A solution containing trimesoyl chloride as a solute in n-hexaneat a mass fraction of 0.1 wt % was formulated. After the formulation wascompleted, the solution was poured on the surface of thepolyethersulfone ultrafiltration membrane treated in step 1 and allowedto completely infiltrate it for 1 minute, and then the organic phasesolution was drained. After the organic phase solution was completelyevaporated, the resulting dye-salt separation membrane was placed indeionized water for storage.

Separation performance test 1: The resulting dye-salt separationmembrane was installed in a membrane separation device in which thedifferential pressure across the membrane was controlled to 0.4 MPa, andit was determined that at room temperature, for a dye-salt aqueoussolution containing 0.2 g/L of Congo red and 2 g/L of sodium chloride,the retention rate of Congo red was 99.28%, the permeability of sodiumchloride was 94.55%, and the permeate flux was 235.4 Lm⁻²h⁻¹MPa⁻¹.

Separation performance test 2: The resulting dye-salt separationmembrane was installed in a membrane separation device in which thedifferential pressure across the membrane was controlled to 0.4 MPa, andit was determined that at room temperature, for a dye-salt aqueoussolution containing 0.2 g/L of Congo red and 2 g/L of sodium sulfate,the retention rate of Congo red was 99.32%, the permeability of sodiumsulfate was 89.90%, and the permeate flux was 235.5 Lm⁻²h⁻¹MPa⁻¹.

Example 3

Step 1: An aqueous phase solution containing a mixture of tannic acidand anhydrous piperazine as a solute at a combined mass fraction of 0.2wt % was formulated. The mass ratio of tannic acid to anhydrouspiperazine in the mixture was 1:1. After the formulation of the aqueousphase solution was completed, the aqueous phase solution was poured on asurface of a polyethersulfone ultrafiltration membrane and allowed tocompletely infiltrate it for 5 minutes, and then, the aqueous phasesolution was drained.

Step 2: A solution containing trimesoyl chloride as a solute in n-hexaneat a mass fraction of 0.1 wt % was formulated. After the formulation wascompleted, the solution was poured on the surface of thepolyethersulfone ultrafiltration membrane treated in step 1 and allowedto completely infiltrate it for 1 minute, and then the organic phasesolution was drained. After the organic phase solution was completelyevaporated, the resulting dye-salt separation membrane was placed indeionized water for storage.

Separation performance test 1: The resulting dye-salt separationmembrane was installed in a membrane separation device in which thedifferential pressure across the membrane was controlled to 0.4 MPa, andit was determined that at room temperature, for a dye-salt aqueoussolution containing 0.2 g/L of Congo red and 2 g/L of sodium chloride,the retention rate of Congo red was 99.42%, the permeability of sodiumchloride was 94.59%, and the permeate flux was 315.2 Lm⁻²h⁻¹MPa⁻¹.

Separation performance test 2: The resulting dye-salt separationmembrane was installed in a membrane separation device in which thedifferential pressure across the membrane was controlled to 0.4 MPa, andit was determined that at room temperature, for a dye-salt aqueoussolution containing 0.2 g/L of Congo red and 2 g/L of sodium sulfate,the retention rate of Congo red was 99.19%, the permeability of sodiumsulfate was 94.59%, and the permeate flux was 273.9 Lm⁻²h⁻¹MPa⁻¹.

Comparative Example 1

Step 1: An aqueous phase solution containing a mixture of tannic acidand anhydrous piperazine as a solute at a combined mass fraction of 0.2wt % was formulated. The mass ratio of tannic acid to anhydrouspiperazine in the mixture was 1:4. After the formulation of the aqueousphase solution was completed, the aqueous phase solution was poured on asurface of a polyethersulfone ultrafiltration membrane and allowed tocompletely infiltrate it for 5 minutes, and then, the aqueous phasesolution was drained.

Step 2: A solution containing trimesoyl chloride as a solute in n-hexaneat a mass fraction of 0.1 wt % was formulated. After the formulation wascompleted, the solution was poured on the surface of thepolyethersulfone ultrafiltration membrane treated in step 1 and allowedto completely infiltrate it for 1 minute, and then the organic phasesolution was drained. After the organic phase solution was completelyevaporated, the resulting dye-salt separation membrane was placed indeionized water for storage.

Separation performance test 1: The resulting dye-salt separationmembrane was installed in a membrane separation device in which thedifferential pressure across the membrane was controlled to 0.4 MPa, andit was determined that at room temperature, for a dye-salt aqueoussolution containing 0.2 g/L of Congo red and 2 g/L of sodium chloride,the retention rate of Congo red was 99.71%, the permeability of sodiumchloride was 72.91%, and the permeate flux was 216.4 Lm⁻²h⁻¹MPa⁻¹.

Separation performance test 2: The resulting dye-salt separationmembrane was installed in a membrane separation device in which thedifferential pressure across the membrane was controlled to 0.4 MPa, andit was determined that at room temperature, for a dye-salt aqueoussolution containing 0.2 g/L of Congo red and 2 g/L of sodium sulfate,the retention rate of Congo red was 99.69%, the permeability of sodiumsulfate was 51.12%, and the permeate flux was 203.9 Lm⁻²h⁻¹MPa⁻¹.

Comparative Example 2

Step 1: An aqueous phase solution containing a mixture of tannic acidand anhydrous piperazine as a solute at a combined mass fraction of 0.2wt % was formulated. The mass ratio of tannic acid to anhydrouspiperazine in the mixture was 4:1. After the formulation of the aqueousphase solution was completed, the aqueous phase solution was poured on asurface of a polyethersulfone ultrafiltration membrane and allowed tocompletely infiltrate it for 5 minutes, and then, the aqueous phasesolution was drained.

Step 2: A solution containing trimesoyl chloride as a solute in n-hexaneat a mass fraction of 0.1 wt % was formulated. After the formulation wascompleted, the solution was poured on the surface of thepolyethersulfone ultrafiltration membrane treated in step 1 and allowedto completely infiltrate it for 1 minute, and then the organic phasesolution was drained. After the organic phase solution was completelyevaporated, the resulting dye-salt separation membrane was placed indeionized water for storage.

Separation performance test 1: The resulting dye-salt separationmembrane was installed in a membrane separation device in which thedifferential pressure across the membrane was controlled to 0.4 MPa, andit was determined that at room temperature, for a dye-salt aqueoussolution containing 0.2 g/L of Congo red and 2 g/L of sodium chloride,the retention rate of Congo red was 99.70%, the permeability of sodiumchloride was 84.41%, and the permeate flux was 98.4 Lm⁻²h⁻¹MPa⁻¹.

Separation performance test 2: The resulting dye-salt separationmembrane was installed in a membrane separation device in which thedifferential pressure across the membrane was controlled to 0.4 MPa, andit was determined that at room temperature, for a dye-salt aqueoussolution containing 0.2 g/L of Congo red and 2 g/L of sodium sulfate,the retention rate of Congo red was 99.59%, the permeability of sodiumsulfate was 66.48%, and the permeate flux was 102.1 Lm⁻²h⁻¹MPa⁻¹.

Example 4

Step 1: An aqueous phase solution containing a mixture of tannic acidand anhydrous piperazine as a solute at a combined mass fraction of 0.2wt % was formulated. The mass ratio of tannic acid to anhydrouspiperazine in the mixture was 1:1. After the formulation of the aqueousphase solution was completed, the aqueous phase solution was poured on asurface of a polysulfone ultrafiltration membrane and allowed tocompletely infiltrate it for 5 minutes, and then, the aqueous phasesolution was drained.

Step 2: A solution containing trimesoyl chloride as a solute in n-hexaneat a mass fraction of 0.1 wt % was formulated. After the formulation wascompleted, the solution was poured on the surface of the polysulfoneultrafiltration membrane treated in step 1 and allowed to completelyinfiltrate it for 1 minute, and then the organic phase solution wasdrained. After the organic phase solution was completely evaporated, theresulting dye-salt separation membrane was placed in deionized water forstorage.

Separation performance test 1: The resulting dye-salt separationmembrane was installed in a membrane separation device in which thedifferential pressure across the membrane was controlled to 0.4 MPa, andit was determined that at room temperature, for a dye-salt aqueoussolution containing 0.2 g/L of Congo red and 2 g/L of sodium chloride,the retention rate of Congo red was 99.58%, the permeability of sodiumchloride was 95.05%, and the permeate flux was 286.3 Lm⁻²h⁻¹MPa⁻¹.

Separation performance test 2: The resulting dye-salt separationmembrane was installed in a membrane separation device in which thedifferential pressure across the membrane was controlled to 0.4 MPa, andit was determined that at room temperature, for a dye-salt aqueoussolution containing 0.2 g/L of Congo red and 2 g/L of sodium sulfate,the retention rate of Congo red was 99.33%, the permeability of sodiumsulfate was 90.96%, and the permeate flux was 272.1 Lm⁻²h⁻¹MPa⁻¹.

Example 5

Step 1: An aqueous phase solution containing a mixture of tannic acidand anhydrous piperazine as a solute at a combined mass fraction of 0.2wt % was formulated. The mass ratio of tannic acid to anhydrouspiperazine in the mixture was 1:1. After the formulation of the aqueousphase solution was completed, the aqueous phase solution was poured on asurface of a polyethersulfone ultrafiltration membrane and allowed tocompletely infiltrate it for 5 minutes, and then, the aqueous phasesolution was drained.

Step 2: A solution containing trimesoyl chloride as a solute incyclohexane at a mass fraction of 0.1 wt % was formulated. After theformulation was completed, the solution was poured on the surface of thepolyethersulfone ultrafiltration membrane treated in step 1 and allowedto completely infiltrate it for 1 minute, and then the organic phasesolution was drained. After the organic phase solution was completelyevaporated, the resulting dye-salt separation membrane was placed indeionized water for storage.

Separation performance test 1: The resulting dye-salt separationmembrane was installed in a membrane separation device in which thedifferential pressure across the membrane was controlled to 0.4 MPa, andit was determined that at room temperature, for a dye-salt aqueoussolution containing 0.2 g/L of Congo red and 2 g/L of sodium chloride,the retention rate of Congo red was 99.34%, the permeability of sodiumchloride was 94.48%, and the permeate flux was 313.0 Lm⁻²h⁻¹MPa⁻¹.

Separation performance test 2: The resulting dye-salt separationmembrane was installed in a membrane separation device in which thedifferential pressure across the membrane was controlled to 0.4 MPa, andit was determined that at room temperature, for a dye-salt aqueoussolution containing 0.2 g/L of Congo red and 2 g/L of sodium sulfate,the retention rate of Congo red was 99.16%, the permeability of sodiumsulfate was 91.68%, and the permeate flux was 294.7 Lm⁻²h⁻¹MPa⁻¹.

What is claimed is:
 1. A method for preparing a dye-salt separationmembrane, comprising the following steps: step 1: pouring an aqueousphase solution containing tannic acid and anhydrous piperazine on asurface of a polysulfone-based ultrafiltration base membrane at a massratio of the tannic acid to the anhydrous piperazine of 1:2 to 2:1,followed by complete infiltration for 3 to 6 minutes, and then drainingthe aqueous phase solution; and step 2: pouring an organic phasesolution of trimesoyl chloride on the surface of the polysulfone-basedultrafiltration base membrane obtained in step 1, followed by completeinfiltration for 0.5 to 2 minutes, then draining the organic phasesolution, and after the organic phase solution being completelyevaporated, storing the resulting dye-salt separation membrane in water.2. The method according to claim 1, wherein in step 1, thepolysulfone-based ultrafiltration base membrane is selected frompolyethersulfone, polysulfone, or sulfonated polyethersulfone.
 3. Themethod according to claim 1, wherein in step 1, the aqueous phasesolution contains the tannic acid and the anhydrous piperazine at acombined mass fraction of 0.2 wt %.
 4. The method according to claim 1,wherein in step 1, the infiltration is performed for a time period of 5minutes.
 5. The method according to claim 1, wherein in step 1, the massratio of the tannic acid to the anhydrous piperazine is 1:1.
 6. Themethod according to claim 1, wherein in step 2, the organic phasesolution of the trimesoyl chloride contains the trimesoyl chloride at amass fraction of 0.1 wt %.
 7. The method according to claim 1, whereinin step 2, the infiltration is performed for a time period of 1 minute.8. The method according to claim 1, wherein in step 2, the organic phasesolution contains a solvent selected from n-hexane or cyclohexane.
 9. Adye-salt separation membrane prepared by the method according toclaim
 1. 10. A dye-salt separation membrane prepared by the methodaccording to claim
 2. 11. A dye-salt separation membrane prepared by themethod according to claim
 3. 12. A dye-salt separation membrane preparedby the method according to claim
 4. 13. A dye-salt separation membraneprepared by the method according to claim
 5. 14. A dye-salt separationmembrane prepared by the method according to claim
 6. 15. A dye-saltseparation membrane prepared by the method according to claim
 7. 16. Adye-salt separation membrane prepared by the method according to claim8.